


Soft Robotics

by isozyme



Category: Avengers (Comics), Marvel 616
Genre: M/M, Masturbation...with help!, Robot Tentacles, Sex Farce
Language: English
Status: Completed
Published: 2020-01-24
Updated: 2020-01-24
Packaged: 2021-02-27 08:35:39
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,324
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22394113
Author URL: https://archiveofourown.org/users/isozyme/pseuds/isozyme
Summary: “I promise this is all non-toxic. The silicone is medical-grade, even.”Steve makes a choking noise. “I would hope so,” he says, going bright, tomato red as he says it.Tony makes some cool robots.  Steve makes an assumption.
Relationships: Steve Rogers/Tony Stark
Comments: 27
Kudos: 372
Collections: You Gave Me A Stocking 2019





	Soft Robotics

**Author's Note:**

  * For [Sineala](https://archiveofourown.org/users/Sineala/gifts).



> Merry Christmas Sine! I know you love tentacles so I wrote some for you -- I hope you enjoy it! 
> 
> Many thanks to Nigmuff and Hopelesse for cheering me on through this adventure.

Tony doesn’t think anything of Steve walking into the workshop. Sure, it’s a giant mess, but within the expected range of workshop messes. It’s not an outlier or anything.

The mess is the result of his current obsession: soft-bodied robots. What if he could harness all the benefits of nature and machine? There’s all kinds of examples: an octopus’s arm can crush a clam’s shell and also delicately tickle its favorite keeper; snakes can get into anything — really anything, Tony thinks with a shudder, remembering the most recent go-around with the Serpent Society — and roundworms might be the most successful organisms on the planet.

He’s designing long, wiggly robots, great for squirming into tight spaces like collapsed buildings or narrow pipes. He’s been thinking of applications in rescue and reconnaissance, mainly, with vague inklings on the horizon about more sophisticated soft robots for arthroscopic surgery.

Now, three days into the project, Tony’s workstations are covered in plaster molds and tubs of silicone. He’s got a mostly-assembled prototype arm clamped to the edge of a bench, going through stress-tests of its servo muscles. He’s worried the metal components inside might wear through the outer flexible skin too quickly, and he might need a different material as a support structure. Maybe he could do it all using hydrostatic forces. Possibly contained by some sort of cloth? Tony waves Steve farther inside and jots that down: _collagen/protein matrix fabric? investigate textiles._

Steve steps into full view of Tony’s creative process and stops dead. “Um, Tony? Is this a bad time?”

“No? Why? It’s fine, nothing time-sensitive running right now, it’s all on automatic for a while.”

There’s something very odd about how Steve is regarding him. He looks like he’d rather be anywhere but here, which isn’t Steve’s usual reaction to Tony working. There are some suspiciously slimy spills, he guesses — it wouldn’t be completely unreasonable for Steve to assume that Tony’s working with dangerous chemicals. There’d been the one time with the hexafluoride, which was memorable.

“I promise this is all non-toxic. The silicone is medical-grade, even.”

Steve makes a choking noise. “I would hope so,” he says, going bright, tomato red as he says it.

Tony checks himself up and down and can’t find anything remarkable. He glances at his computer monitors — nothing weird, just his schedule, email, and a couple CAD renderings of octopus muscle structure spinning lazily while they wait for the 3D printer.

“Do you not like my soft body robotics experiments?” he asks finally, at a complete loss.

“So…that’s a robot? Not a — um —” Steve says, still strangled and blushing furiously.

“One of several robots prototypes,” Tony agrees, forging ahead despite the weird signals from Steve. “Watch this, it can go through a pipe that’s partially blocked by debris.” He unhooks his prototype from its stand and sets it in front of the obstacle course he’s built to challenge his creations.

The robot squeezes gamely into the narrow opening, wriggling determinedly forward. Steve goes, impossibly, more red.

“Isn’t it great? These are going to be cheap, rustproof, waterproof, and super energy efficient. I’m running this one on what’s basically a watch battery.”

“It’s swell, Tony,” Steve says, eyes wide, strangely transfixed by Tony’s robot still working its way into the pipe.

Tony ducks down into Steve’s line of sight, frowning up at him. “You’re being weird, Winghead. Is everything okay?”

Usually people don’t get alarmed by his robots until they’re substantially more dangerous than this.

“It’s nothing, really, I just thought for a second you were building something, ah, hm.”

“What?”

“Something — custom. For, um, personal use.” Steve makes an abortive gesture and then looks down at his hands, horrified. Then his face hardens in resolve, jaw squaring up like he’s Captain America about to face down an army. He clears his throat.

“I thought I walked in on you making yourself a tentacle dildo,” Steve says, voice firm and clear as a bell. “I didn’t mean to insult or make you uncomfortable. Human sexuality is naturally complex.”

_Oh god._

_Oh god oh god oh god._

_Steve knows what tentacle porn is._

_Steve knows what tentacle porn is and he thinks I’m into tentacle porn._

_I don’t know how I’m going to recover from this._

Tony straightens up and coughs into his hand. “That would be quite the off-label use,” he says, trying to turn it into an easy joke, ha ha, a little sex mistake between best friends, and not confident he sticks the landing on the dismount. “These are strictly for, ah, non-invasive applications.”

“Right. In that case -- I guess I’ll just -- leave you to it,” Steve says, confident facade starting to fray, and then he bolts.

* * *

If you’d asked Tony twelve hours ago, he would have told you he wasn’t interested in any kind of tentacle anything. He’d watched some really shocking porn on a dare in his youth, it wasn’t like he didn’t _know_ about the genre, but he’d been confident it wasn’t for him.

Now, maddeningly, it’s all he can think about.

He has to put the soft robotics project on hold while he figures this out, because he can’t work if he’s popping a semi every time he picks up the damn thing to rewire it. Instead, he sits in his workshop and tries to comment up some code he wrote in a mad all-night rush a few weeks ago. He needs to focus to untangle his past self’s leaps in logic.

_Steve thought about a tentacle going up your ass. He looked at your robot and the first thing he thought about was it inside you._

Did Steve think about the whole fisherman’s wife she-bang? Tony strung up in tentacles and writhing as he took it in every orifice? Tony has first-hand experience with hostile tendrils of all kinds, but hadn’t connected them to anything erotic.

Until now.

Tony groans and puts his face into the keyboard.

Maybe Steve was projecting. Tony thinks this possibility will be comforting until he starts imagining _Steve_ covered in fucking tentacles — literal fucking tentacles — all naked and flushed and bucking against the intrusion, or maybe bucking towards it, wanton and desperate and Tony’s half-hard in his pants again, goddamnit.

Tony’s a problem-solver. He can solve this.

Maybe the way to get past the tentacle distraction isn’t avoidance but desensitization. He’s obsessed with the novelty of it, the lure of the unknown, and if he just tries it a bit his dick will come to its senses.

“Sorry buddy,” he says to his robot. “I’m afraid I have to retrofit you in the service of impure acts.”

The robot doesn’t respond, because it’s a robot and doesn’t have an opinion on the matter.

Tony’s a great engineer, so he’s going to make a great sex toy. That’s a given. There’s no project he hasn’t given his all. Maybe the nose armor could have used a little more attention to detail, but every other project: maximum effort.

In Steve’s defense, the robot doesn’t need many adjustments to turn it into a dildo. It wasn’t such a spectacular leap. Tony writes down a list of essential features on a scrap of paper:

  * _Aesthetically pleasing_
  * _Lube-compatible (prob. water based), sterilizable_
  * _Ergonomic and autonomous_
  * _Not going to permanently injure my ass_



For aesthetics, he’ll change the silicone from neutral translucent white to a nice glossy black, and add some surface detail. Lube and cleanup are minimal concerns; medical grade silicone is a popular sex toy material already. The programming needs the most work and will demand some finesse, both to teach the robot how to find the prostate, and to address the no-busting-Tony’s-butt requirement.

Tony cracks his knuckles and goes to drag his much-abused life-size crash test dummy out of its crate. He tosses it onto the couch and knocks its knees wide. It looks both pathetic and debauched. Using a bit of scrap tubing and baling wire, Tony rigs up a stand-in for the new toy, then gets to work on the logistics and choreography, as it were.

* * *

What Tony ends up making is a four-foot-long tentacle, slick and dark and very slightly menacing. It has a heavy base that can be bolted or clamped to basically anything. When it can’t sense anything at a human body temperature within its radius, it lies quiescent, but step within its reach and it perks up, hungry for simulated nookie.

Tony lets it grope his thigh for a bit before deciding he’s satisfied.

Then he makes two more, because it’s good design sense to have multiple prototypes.

By the time Tony’s done with all that, he’s so sick of troubleshooting the damn things his dick has decided it’s completely uninterested in the proceedings. Success!

Tony shuts everything down and heads upstairs to rustle up some lunch. When he’s back in a place with windows, it turns out he’s misjudged “lunchtime” by about seven hours. Conveniently, this lands him right in the middle of dinner.

He sniffs around for food and finds Clint, Thor, and Steve in the dining room, demolishing a gigantic platter of sushi. Tony winces as Clint stabs a piece with a fork and pops it into his mouth. Steve and Thor have manners and are using chopsticks.

Thor beckons. “Come eat!”

Tony’s always liked sushi. He appreciates the expertise hidden within its simplicity. Fish, rice, nori. Three basic ingredients; ten years of training to master them.

It also tastes great.

Tony is about to sit down and enjoy some of the nice fresh tuna belly when he watches Steve pick out a piece of tako sushi and pop it in his mouth.

Steve eating octopus is _not what Tony needs right now._

His dick wakes up with a vengeance and all Tony can think is _mouth tentacle ass tentacle Steve tentacle._

“I better not,” Tony says, stopping dead in his tracks. “Stomach upset, can’t do fish right now.”

“Is there anything we can get you?” Steve asks, making to stand up.

“No!” Tony says. “I’m fine! I’ll be fine!”

Steve smiles at him and Tony’s traitor cock informs him that Steve has a great smile. It also informs him that Steve would look great with his lips wrapped around Tony’s new tentacular creations downstairs, or around Tony’s cock while a robot tentacle worked its way in and out of his ass. Tony needs to leave right now or things are going to get obvious.

Scratch that, things are already obvious. If Tony wants to go up to his room to solve this problem, he has to walk around the table with his crotch in full view of his fellow Avengers. So Tony does the only sensible thing and turns right back around and goes to his workshop.

He can take care of this there. There’s three custom-built kinky sex robots in the workshop, designed to address exactly this problem. He’ll just head downstairs, drop trou, and do a few practical tests.

* * *

It takes some trial and error, but Tony thinks he has it. All three tentacles are lubed up and bolted to something sturdy, Tony is naked except for a white undershirt that’s rucked up around his ribs, and he’s sprawled comfortably on his napping-couch.

“System go for testing,” Tony says, and his robots snap to attention. One squirms up against his hot-and-bothered cock. Instead of wrapping around it and stroking, the tentacle plucks at his skin with its suckers.

“Weird sensation, Number Three,” Tony tells it. The learning program needs a little more feedback from something that isn’t a badly singed crash test dummy.

In response, Three changes tactics and attaches itself to the delicate skin of Tony’s inner thigh and latches on, suckers pulling hard. Tony feels the hot prickle of bruises forming. “Good,” he says, voice gone breathy already. “Reinforce behavior.”

For a torturous span of minutes, all the tentacles want to do is suck neat rows of round hickeys up and down Tony’s legs and chest. “I can’t take this much longer, I’ll pop,” Tony pants finally. “Introduce some entropy, up the parameters for novelty-seeking.”

The tentacles abandon their hickeys and go roving for new fun spots. One finds a nipple, Three finds his dick again, and Two makes a foray down under. “That’s the stuff,” Tony says. “Iterate at about four and a half degrees of freedom, guys.”

Number Two delicately pushes at his ass, and Tony holds his breath. This is the part that could go very bad very fast. The hydraulics inside the mechanical arms could easily exert injurious force, and while Tony was careful about his code, there’s still a moment of thrill as he waits for it to perform.

Then there’s a slick, intrusive slide, and Tony’s mouth falls open. It’s not quite like fingers or other toys. Purposeful, but alien. “Yep, good, full speed ahead,” Tony gasps.

That’s all the encouragement the tentacle needs to start pounding him into the couch cushions.

 _Oh, fuck, this was a terrible plan,_ Tony thinks, because there’s no way he’s going to be able to stop obsessing over this.

Then someone knocks on the door.

“Full stop!” Tony commands.

Obediently, his tentacles freeze. He’s built them so they could stop on a dime, which is working great. What he hadn’t developed was what they should do after they stopped. He doesn’t want anything to tear if a startled robot decided to jerk away, so for the time being they respond to his safety command by locking up instantly. Had it just been one tentacle, as originally planned, it wouldn’t have been too hard to wriggle free. However, when Tony scaled up to three, he forgot to revisit the issue.

He’s effectively pinned to the couch, like a rare beetle on specimen board.

“Tony?” someone calls, and it’s Steve. Of course it’s Steve, Steve who thinks Tony is into tentacle porn is visiting Tony’s workshop while Tony is fucking himself with tentacles and he’s going to get absolutely the wrong idea.

Or possibly the right one, Tony thinks with a wince, considering how much he’d been enjoying himself.

“Don’t come in!” Tony shouts.

“Tony, are you all right?” Steve asks through the door.

“Peachy!” Tony’s weight shifts as he says it, causing his voice to break over the middle of the word.

“I wanted to check on you,” Steve says. “You said you didn’t feel well earlier, and I know how you can be about getting sick.”

Tony groans, and then realizes all too late that Steve will interpret the noise as evidence that Tony needs assistance. Sure enough, Steve’s keying in his password and pushing open the door.

Tony sighs as Steve comes into view.

“Before you ask, this time it is exactly what it looks like.”

Steve stops dead in his tracks. Then he very carefully puts down the tray he’s carrying -- with what looks like soup and saltine crackers on it, Steve’s so sweet and Tony is so, _so_ aware of the thick silicone in his ass -- and tries valiantly to look anywhere but Tony.

“Are you okay?” Steve asks, sounding more strangled than he does while actually being choked out. Usually by tentacles. Tony could program breathplay into his artificial tentacles, actually. The thought makes his dick twitch within its coil of tentacle. It would be safer than the usual ways, honestly -- he’s already halfway-designing a blood-oxygen saturation monitor that could be built into the suckers when he remembers that Steve is still staring very resolutely at Tony’s drill press.

Tony knows what kind of _drill press_ he wants from Steve.

His brain must completely blasted on embarrassment and endorphins if he’s making puns this awful.

“I’m good,” Tony says, weakly waving a hand. He’s going to reassure Steve more, but he’s forgotten a key fact, which is that he’s designed the artificial intelligence recognizes “good” as a green light to resume going to town on him. He should have picked a control word like “polyacrylamide.”

Tentacle Two pulls out of his ass with a long slurp and thrusts eagerly back in. Tony whimpers.

“There’s still some kinks to work out,” Tony tells Steve.

_Kinks. Ha! I’m hilarious._

“Not a go, you stupid sex robot, repeat, not a go.”

Tony’s about five seconds away from breaking out into helpless, mortified cry-laughter. The tentacles wrapped around him halt their ministrations, but he’s still sticky and full and prickling all over with the desire to get fucked senseless.

Steve makes a small pained sound. Tony looks at him in helpless apology. Poor Steve, standing there in his Avengers 5k Fun Run extra-large t-shirt and comfiest sweatpants, the kind of thing he wears when he’s looking forward to sitting down on the couch and turning on a dumb fantasy flick. Tony had promised him a Princess Bride re-watch earlier that week -- Steve had probably been planning to ask Tony if he wanted to hang out on the couch with a movie until he felt better.

Taking stock of Steve’s sweatpants yields the unexpected fact that Steve is really, really hard.

_Oh. Ohhhhhh shit._

“Or,” Tony says carefully, “it could be a go. They respond to vocal commands, and aren’t keyed to my voice in particular.”

“That’s interesting,” Steve whispers.

Tony holds his breath. This is possibly the most vulnerable he’s ever been in his life. He’s mostly naked, speared on a very large, _very_ non-standard dildo, and he’s just propositioned Captain America, a man he’s been attracted to for longer than he likes to contemplate. Maybe more than just attracted to.

Steve’s not staring determinedly into the middle distance anymore. He’s fixated on Tony, gaze traveling in a loop from his face, down to the fun zone, and back up. He doesn’t seem repelled. He looks -- almost -- like he might be game for this.

Tony’s life is so weird.

“So if I tell them to start fucking you again--” Steve ventures, taking a tentative step forward.

The tentacle in Tony’s ass wriggles in response. “Yep,” Tony gasps. “They’ll be happy to oblige.”

Steve’s pupils go wide and dark. It’s not like Tony’s never imagined making a pass at Steve. He just never imagined it going quite like this. Steve moves like he’s not entirely sure how his feet are attached to his body, stumbling toward Tony until he can fall, graceless, into a swivel chair barely a foot away from the couch. If he moved just a few inches, his knee would graze against Tony’s. His hard cock is an obvious line down his left leg. Now Tony knows which way Steve dresses.

“Get on with it, then,” Steve says, nodding to the tentacles like they have a business relationship. Tony whines as things get intense again, very fast.

It was a lot when Tony was on his own, letting his new toys do as they pleased with him. With Steve at the wheel it’s a thousand times more. He feels the thrill of being taken, giving it up to somebody else. Even better, now instead of giving it up to his own brilliant engineering, he’s giving it up to _Steve._

Steve’s hands are clamped onto the armrests of his chair, knuckles bone-white.

Tony traces the line of sucker-marks that trails from his right nipple down to his opposite hipbone, enjoying the sting as he scrapes a bit with his fingernail. That’s nice. Even nicer is the way it makes Steve’s cock twitch in his pants.

“Hold his -- hold his thighs open. I want to see,” Steve requests, gaining confidence, starting to settle into a mindset where this is about sex, not an experiment that’s landed a teammate in an awkward predicament. God, Steve is such a top. Tony hadn’t thought about it in exactly those terms before but it’s obvious now why he’s great at it. It makes sense that Steve could take his easy command in the field and transform it into something unbearably hot.

“Do you want to touch yourself?” Tony asks, because in Steve’s position he’d be dying for a hand on his cock. “I don’t mind. Obviously.”

“Yeah,” Steve says, and pulls his dick out with a sigh of relief. “That’s -- you look real nice, Tony.

“You think so?”

“This is kind of a custom-made fantasy for me,” Steve says, then blushes hard. “Maybe you didn’t need to know that.”

“You want me to make more of these?” Tony asks, breathless. “I could have them hold me down, if you like. Put me exactly where you wanted. You’ll find they’re very flexible, and so am I.”

Steve groans and works his cock faster. “Can you take it harder?”

“Try me,” Tony says, absolutely one hundred percent game for that.

“Deeper,” Steve tells the tentacle inside Tony, voice gone husky.

It complies, getting thicker as it goes. Tony arches his back and welcomes it, Steve’s gaze on him so heavy with intent that it’s like a physical object sliding over his skin.

* * *

Steve tries _everything._ He’s creative, completely tuned into Tony’s responses, and a little evil. Tony’s a gasping wreck, hands flexing open and shut on nothing as he feels orgasm starting to build in an insistent, inevitable way.

Tony wants Steve to be touching him while he comes. It’s a hopeless desire, because they haven’t -- for all of the sex stuff happening, it doesn’t quite seem possible that Steve would want to touch Tony skin-to-skin.

He must reach out, give some inadvertent sign what he wants, because Steve stands up on shaky legs. To Tony’s surprise, Steve picks his way around the whirring, thrusting mess of tentacles sprouting from the workshop floor and climbs onto the sofa. He straddles Tony, one hand braced on the back of the couch and one attending to his own flushed cock.

“This okay?” Steve asks.

Tony nods. Steve fills his entire field of view, a broad expanse of chest and shoulders. Tony feels simultaneously overwhelmed and so, so safe. “It’s good, really good, perfect.”

The robots hear him and increase their efforts.

“Unh, fuck, ngh,” Tony grunts. Stupid over-enthusiastic learning program.

“Slow it down, boys,” Steve says with a chuckle. “You’re going to wear him out.”

“Thanks,” Tony says as the tentacles adjust to a more langid pace.

Steve smiles at him and strokes his fingers through Tony’s damp hair. “You’re doing amazing, handsome,” he says. Tony turns helplessly into the touch, glowing under Steve’s praise, savoring every second of it. “Look at you.”

“Gonna--” Tony rasps, hips bucking as a clever tentacle nails his prostate again. Sweat is beading on his forehead, running in tickling paths down into his goatee.

“I know,” Steve says.

Then Steve abandons stroking himself and folds one big hand around Tony’s cock instead. Tony cries out because it’s perfect; Steve’s been paying attention to what he likes and replicates it exactly. He thinks he might cry, it’s so good.

It doesn’t take much -- a few strokes of Steve’s hand in time with the tentacles sliding over and inside of him, and Tony’s punched in the gut with orgasm.

He shakes as it hits him, and through the haze he hears -- or maybe feels -- Steve draw in an astonished breath. “Tony,” Steve says, soft and almost reverent.

Then he dips his head and they’re kissing, Steve’s lips gentle on Tony’s as he shudders through the aftershocks. Tony finds just enough strength to grab Steve by the back of his neck and hold him there.

“Let me, let me,” Tony pants, reaching down blindly to find Steve’s erection. Steve gasps as Tony gets a grip on him, and Tony kisses him and kisses him as he pumps Steve frantically. The toys Tony made are still playing with his softening dick and sore ass, torturing him on the edge of overstimulation, but he doesn’t want to stop even for a second to tell them to back off, not when he has Steve right here and on the brink of orgasm.

Steve finishes with a groan so deep it’s almost a growl. Come lands hot and wet on Tony’s stomach, marking him as Steve’s.

When he’s spent, Steve sags, chest heaving like he’s sprinted up twenty flights of stairs, until his face is tucked into the sweaty crook of Tony’s neck.

Tony strokes Steve’s back, amazed at what they just did.

“All done, robot friends,” Tony says. “Stage an orderly retreat, please.”

Tentacles one and three draw carefully away from Tony’s junk. Two takes its time vacating Tony’s ass, leaving him feeling very soft and open. He almost wishes he’d had the presence of mind to have Steve’s dick replace the tentacle at the end and come inside him; he was plenty prepared. It would have been a sweet, easy slide. He bets Steve would’ve liked it.

It’s probably for the best they didn’t. That might have been moving a bit too fast.

 _I think we’ve already cornered the market on too fast, hm?_ Tony thinks wryly to himself.

“That happened,” Tony says carefully.

“Mmmmmm,” Steve says. He sounds deeply content. He’s getting kind of heavy, but Tony doesn’t mind. Steve smells like warm sweat and a bit like come. Tony could spend eternity getting post-coitally squashed by Steve and be perfectly happy.

“So...when you said this was a custom-made fantasy for you,” Tony continues, “did you mean just the tentacles stuff? Because I can make you as many of these wriggly robot wonders as you like. I’ve got the workflow down.”

“Oh,” Steve says, lifting his head, sounding a touch bereft.

_Hell with it._

“Or,” Tony says, lifting a finger to hush Steve, “was there a more person-specific component?”

Steve’s face lights up with hope like a magnesium flare. He nods, eyes sparkling.

“This is officially the strangest way I’ve ever asked someone out,” Tony says. “But if you wanted to help me test future iterations of this project, I’d like that.”

A bright grin spreads across Steve’s face. “Only if you let me treat you to dinner first.”

* * *


End file.
